1. Technical Field of the Invention
The present invention provides a three dimensional (“3D”) image projection apparatus that can be combined with a single light source projection system, and enables a viewer to perceive a three dimensional projected image while using passive eyewear. A polarization scheme, compatible with both front and rear projection digital light processor based projection systems, as well as frame sequenced projection systems, is described herein.
2. Description of the Prior Art
FIG. 1 shows a prior art 3D imaging system that illustrates several fundamental requirements for 3D image projection. Two two-dimensional (“2D”) images of one scene are displayed, such as by projection apparatuses 101, one of which is slightly different than the second in terms of a line of sight perspective. These perspectives typically define a left eye view and a right eye view. This normally requires dual image recordation in order to provide the two perspectives, or views, as described above, of the same scene. However, such perspectives could be digitally processed, or manually generated. FIG. 1 illustrates two projectors 101 one of which projects a left eye perspective of a scene while the other simultaneously projects a right eye perspective of the same scene. Although simultaneous projection requires two projectors, it is possible to implement a single projector in a 3D imaging system by rapidly alternating the left and right eye perspectives during projection.
Another theoretical requirement of conventional 3D imaging systems is to expose one of the projected perspectives to substantially only one of either the left or right eye and to expose the other of the projected perspectives to substantially only the other eye, such that each projected perspective is seen substantially exclusively only by one eye. The term “substantially” is meant to convey that the image exclusivity be sufficient to induce a 3D perception in the viewer. Thus, with a dual simultaneous projection system, one eye of a viewer will be substantially blocked from seeing the image content from one of the projectors and the other eye will be substantially blocked from seeing the image content from the other projector.
This blocking, often referred to as extinction, can be accomplished in two steps. First, each of the simultaneously projected images is polarized at a different polarizing angle by projection through separately angled polarized transparent media 102. The viewer wears passive polarized eyewear 103 whose lenses are also offset polarized such that one of the lenses will block a first one of the polarized projected images and the other lens will block the second one of the polarized projected images. The physics of polarization, particularly overlapping transparent polarized media, is sufficiently known by those skilled in the art and is not described in detail herein. Prior art methods of providing two different projected perspectival images to a viewer include coloring the projected images using red and blue color coding combined with passive eyewear having a blue and a red lens that is worn by the viewer.
There have been many attempts to generate 3D image systems. We are concerned here with 3D imaging in systems which use polarization encoding of the left and right eye views, which may be implemented using a switched system. Modern front and rear projection color imaging systems, such as DLP technology, employ multiple color filters to sequentially project elements of a full color image onto a screen. These color filters are typically implemented as segments on a color filter wheel, which spins at a rate synchronized with the input video stream. Typically, this approach uses the three basic video imaging colors (red, blue, and green) in combination with a high brightness white light source. In order to facilitate white balance of the image and correct for certain kinds of image aberrations, a transparent filter segment is often incorporated into the color filter wheel, allowing white light to pass through.
In order to modify these imaging systems so that they support the transmission of stereoscopic three-dimensional images, it is necessary for them to provide separate left and right eye views. The separate eye views can be provided by separate image streams that are combined into a single stream of digital image data and by alternating the projection of image data between these image streams to provide the left and right eye views to the viewer and using an additional filtering apparatus, which may or may not be part of the same color filter wheel used in the projector. In this case, it may become necessary to synchronize the phase, frequency, and possibly other attributes of the rotating color filter wheel with an external stereoscopic imaging element. This synchronization is not necessarily always achieved simply by accessing the electronic signals used to control the color filter wheel.
Published patent application US 2005/0041163A1 describes the use of a segmented polarizer attached to the color filter wheel inside a digital light processor (“DLP”) projector. It does not describe any required relationship between the projector lens optics and an alternating polarizer with respect to polarization sensitivity. Thus, the projection lenses and other optics may corrupt the polarization encoded image signal. Details of the synchronization required between the filter wheel and polarization wheel are not described, nor is there any reference to the distinction between frame sequential and other types of video input. This prior art will not work for all types of video input such as line interleaved video streams. The above-identified patent application is incorporated herein by reference in its entirety.
U.S. Pat. No. 5,993,004 describes a stereoscopic display with a spatial light modulator and polarization modulator, using polarization preserving optics and special control signals for the modulation. As a general statement, this approach does not use alternating polarization as our invention does. The above-identified patent is incorporated herein by reference in its entirety.
Published U.S. patent application 2005/0046700A1 describes two video processing devices which process at least four separate sequences of video images for projecting multiple image views on a screen simultaneously. At a high level, this approach does not use alternating polarization as our invention does. The above-identified patent application is incorporated herein by reference in its entirety.
Published U.S. Application 2003/0112507 describes two embodiments for DMD devices, both of which use different rows or columns of the DMD device driven sequentially to provide different eye views of the same image. This approach is not related to the use of alternating polarization as our invention is. The above-identified patent application is incorporated herein by reference in its entirety.
Published U.S. application 2003/0214631 describes a projector with a beam splitter to produce two light paths, each of which passes through a fixed polarizer and are later recombined with a special optical system. This approach does not use alternating polarization as our invention does. The above-identified patent application is incorporated herein by reference in its entirety.
U.S. Pat. No. 1,879,793 describes the original motion picture projection system (similar to those later used in IMAX 3D applications) in which the rate of film passing through the projector is synchronized in some fashion with an external polarizing wheel or slides. This approach requires special film processing techniques. The above-identified patent is incorporated herein by reference in its entirety.
In the personal computer (“PC”) industry, liquid crystal display (“LCD”) optical shutter glasses have become the standard for cathode ray tube (“CRT”) and projector viewing for color 3D imagery. However, this requires active eyewear (with a miniature liquid crystal monitor or shutter in each lens), as well as requiring a battery and connection to the data source for synchronization purposes. These solutions also tend to be expensive, are only practical for a limited number of users at one time, and tend to induce eye strain after prolonged use. These glasses typically use the Display Data Channel industry standard contained in every modern video adaptor card interface. This data channel signals the glasses that the PC has swapped its eye view.
In general, the prior art requires the projector to use internal optics which are polarization insensitive, since the light polarization must be maintained from the filter wheel through the rest of the projection path. This means that special optics must be used, and polarization sensitive coatings must be avoided, thereby increasing both the complexity and implementation cost.